Various combustion processes are understood to take place in internal combustion engines. The control and regulation of the so-called HCCI combustion process for gasoline engines (homogeneous charge compression ignition is also known as gasoline HCCI or controlled auto ignition—CAI). HCCI refers to a lean combustion process aimed at a significant reduction in consumption, amounting to 10-15% of fuel in the automobile (by dethrottling the engine operation and by thermodynamically favorable combustion) without significant untreated nitrogen oxide emissions (the 3-way catalytic converter does not reduce nitrogen in lean operation) and thus also without having to accept additional costs for exhaust gas aftertreatment.
Since the gasoline fuel and the compression ratio of a gasoline engine are designed in such a way that self-ignitions (knocking) are prevented as much as possible, the thermal energy required for the HCCI process must be supplied in another way. This may be accomplished in various ways, e.g., by retention or recirculation of the hot internal residual gas or heating of the fresh air. In the present case, a method using exhaust gas retention and recirculation is taken as a basis.
Carrying out an HCCI combustion process requires a number of functionalities of the internal combustion engine, in particular direct injection, a (partially) variable valve gear (e.g., phase adjustability and 2-point lift) as well as an acknowledgement from the combustion (e.g., combustion chamber pressure, structure-borne noise, ionic current, high-resolution rotational speed signal, etc.).
In this context, the engine control must be expanded by adding specific functions for both steady-state control and regulation of HCCI combustion as well as for dynamic control and regulation (load changes and switching of operating modes). The object of steady-state control and regulation is to maintain/set the operating point, cylinder balance and compensation of environmental influences. The object of dynamic control and regulation is to permit the quickest possible load changes and thereby not allow either knocking or misfirings.
The HCCI combustion process requires careful coordination between control and regulation of the combustion itself as well as air system states in the intake manifold to achieve the consumption advantages described here with acceptable pollutant emissions at the same time.
In the wake of the so-called basic application, corresponding values are determined for the control variables (e.g., throttle valve, EGR valve, injection timing and quantity, valve settings (e.g., opening and closing angles) for the intake and exhaust valves, etc.).
In this context, however, it is problematic that there is a high sensitivity of the combustion with regard to environmental conditions, fuel quality and fuel composition, operating history (high/low load), etc., even in steady-state HCCI engine operation. In addition, different interfering effects and marginal effects occur individually for each cylinder (uneven EGR distribution, different internal/external cylinder wall temperatures). It is difficult to acquire data for the control engine characteristics maps because the optimal values are subject to fluctuations both in the short term (e.g., fuel quality) and in the long term (e.g., component aging).
Suboptimal operating phases occur briefly during dynamic HCCI operation (e.g., load change) because the control actions are subject to a deceleration to varying degrees due to the hardware. This is due to the fact that air system states follow the intake manifold dynamics and the phase adjusters are subject to down times as well as being rate-limited, while the injection system may be corrected from one cycle to the next and thus offers the best opportunity for rapid control action.
It would be desirable to deal with these problems.